The present embodiments relate to a method and an apparatus for determining a beam parameter of an asymmetrical photon beam generated by an accelerator.
Accelerators are used in the field of medicine for beam generation. Linear accelerators (Linacs) may be used. Linacs generate electrons or, as secondary and/or braking radiation, photons for the used beam. The generated beam may be used for both diagnostic and therapeutic purposes.
Depending on the requirements specified by the respective application, the beam of the accelerator is shaped differently. The shaping may be performed using collimation and absorption. Aside from symmetrical beam profiles (e.g., with respect to a central axis of symmetrical beams), which may result in a dose profile that is symmetrical with respect to an isocenter, asymmetrical beams are also used. For example, numerous small fields are used instead of an expanded field in beam therapy in modern irradiation techniques such as Intensity Modulated Radio Therapy (IMRT). The numerous small fields surround a tumor to be destroyed and produce a better dose distribution in the tumor.
One procedure for generating asymmetrical beams is specified in WO 98/35358, for example.
The asymmetrical beams are described and/or classified for the use.
Parameters are defined for beam description purposes. The parameters are used almost continuously in the accelerator technique. These parameters include the parameter field size (field size and/or field expansion), penumbra, symmetry and flatness. With asymmetrical fields, a displacement of the field may be performed for evaluation and/or analysis purposes such that the center of the field of the asymmetrical field lies on the central axis.